In a conventional I.S. type machine for the production of glass containers, such as bottles, jars etc, molten glass is fed in the form of gobs which are distributed by means of a distributor to the individual forming sections (generally eight). The containers formed in each of the individual forming sections of the machine are deposited while still hot first on the dead plate of the respective section and from there pushed up to a transfer conveyor called a "carriers" which moves the containers from all of the sections up to a "transfer" placed at the end of the carrier. The transfer separates the containers uniformly and changes the direction of their travel 90.degree. placing them one by one equally spaced in a row on a cross conveyor. Once a complete row of containers is formed, a transfer device on mechanical pusher apparatus simultaneously transfers an entire row from the cross conveyor to the linear conveyor of a lehr. In general, pushers to transfer bottles from the cross conveyor to the lehr use a rod which when moving in the direction of advance of the lehr conveyor simultaneously moves a row of bottles from the cross conveyor to transition dead plates and finally to the linear conveyor of the lehr. The pusher cycle continues with a vertical movement of the rod to allow its return over a new row of bottles which will be introduced to the lehr in the next cycle. While in its retracted position, the rod descends before again beginning its advancing movement.
Such pushers generally comprise a support base, a drive system which comprises a motor working in synchronous operation with the machine and with the lehr and a pushing system comprising two tracks in which two arms holding the pusher rod are mounted for sliding movement and whose arms are moved by cams, connecting rods and cranks designed to impart the desired transfer path to the pusher rod.
In the bottle transfer process with the conventional pushers, a high loss of bottles occurs because the pusher knocks over a certain number during the pushing portion of its cycle. The percentage of bottles lost during the transfer process can be rather high because the bottles are still hot and in falling off the conveyors (knocking over adjacent ones in the process) are susceptible to breaking, deforming or inadequate tempering which means that they will have to be discarded. In order to minimize this problem, a series of advances have been developed both in the apparatus and in the transfer paths. In many pusher designs, during the advance period, a velocity component is imparted to the pusher rod in the direction of movement of the cross conveyor. This reduces the sliding relative movement between the rod and the bottles because the rod moves diagonally over the cross conveyor. Ideally this velocity component should be equal to the velocity of the cross conveyor but in general, such condition is not effected.
A common method to obtain a diagonal path of the rod, is by means of some additional cam and guides mechanism generally horizontal such as in the case of the mechanisms described in U.S. Pat. Nos. 1,437,455 of Mingle, 3,040,867 of Posten, 3,184,031 of Dunlap, 3,277,994 of Giusti, 3,853,213 of Lehman and 4,067,434 of Mumford.
Some pusher apparatuses such as those described in U.S. Pat. Nos. 1,436,455 of Mingle, 2,217,982 of Heil and 2,601,914 of Davies have mechanisms which produce an orbital path of the pusher rod in an horizontal plane. During the pushing of the bottles, as well as during the retraction period, the rod has a velocity component in the direction of advance of the cross conveyor. For example, in the system described in U.S. Pat. No. 2,601,914 of Davies, the pusher rod comprises the central member of a mechanism of four rods. Such mechanisms have the advantage of being simple and not requiring a vertical movement of the rod even when the range of adjustments in displacement is not too great.
To reduce the area occupied by the bottle transfer systems designs have been realized where the mechanism of the pusher is placed over the lehr as in U.S. Pat. No. 2,601,914. The disadvantages of such an arrangement are that the mechanism is difficult to reach by the operators and is exposed to high temperatures.
One other refinement incorporated in some pushers is a stabilizer strip for long and slim bottles. Said strip is positioned during the pushing period slightly beyond the upper part of the bottles to prevent them from inclining and falling forward. Two devices of this kind are described in U.S. Pat. Nos. 2,203,385 to Figel and 3,040,867 of Posten.
An aspect that has received little attention is the synchronization between the "transfer" and the pusher apparatus. It is frequently observed during the operation of a conventional pusher apparatus that the last bottle of a group that is being moved into the lehr is not pushed properly because it remains partially out of the path of the pushing rod. The result is that such bottles stay between the cross conveyor and the dead plates of the lehr obstructing the next group of bottles and sometimes causing them to break. In the system of U.S. Pat. No. 3,853,213 of Lehman, a solution is presented wherein the "transfer" is effected by a pusher device which functions in response to a signal from the I.S. machine. A counter sends a signal to the pusher to initiate its operation when a predetermined number of bottles have accumulated on the cross conveyor.
A concept that has been proposed for high production levels is that of the double pusher where two pusher rods operate alternately. U.S. Pat. No. 4,003,464 of Zappia describes a system that according to its inventor allows machine operation of up to 35 cycles per minute.
In the pusher of the catalog of the Shepee Motor and Engineering Co., Ltd., York, U.K. part of the pusher rod (in the side where the bottles arrive over the cross conveyor) rotates during the retraction period around the horizontal shaft aligned with the length of the lehr in order to avoid interfering with the bottles that are advancing over the cross conveyor. In the same pusher almost all of the delicate mechanical parts are protected by covers.
The pusher apparatus of the catalog of Hydro-Glassomat of Standard Hydraulik, GmbH, Shmarrie, German Federal Republic, represents an advanced technology where the displacements of the pusher rod are produced by hydraulic cylinders controlled by an electronic system allowing a diversity of adjustments. The beginning of the cycle from the retracted position responds to a signal of a sensor in the cross conveyor or of a remote synchronization system. The pusher rod starts its advance and after a predetermined time, the transverse movement is initiated. At the moment the rod reaches its extreme position into the lehr, the action of an adjustable timer is initiated to control the starting of the vertical movement of the rod. At the moment that the extreme vertical position is reached, the retraction movement is initiated and another timer is activated in order that after a predetermined time, the rod returns to the the initial vertical position. The velocities of the displacements in the three different directions can be adjusted independently by means of valves for the oil fluid control.
Instead of pushing the bottles from the cross conveyor to the lehr conveyor, some machines raise them from the cross conveyor and deposit them over the lehr conveyor. This can be done for individual bottles or for groups of bottles as in the apparatus of British Pat. No. 1,313,867 of Jaeger et al.
A device which apparently is in its intial development stage is that analyzed in the reference K. F. Hahn Oberkirchen, "Getrieanalize einer Bogens chubkurbel fur einen neuen kuehlofeneinschieber" Glastenchniber, Vol. 51, No. 3, 1978 pp. 48-54. This device uses a four rod mechanism which achieves a transfer path of the bottles over a circular arch of a little less than 90.degree.. The direction and initial velocity are the same as those of the cross conveyor and the last section and velocity coincide with that of the lehr conveyor. It is not explained how more than a bottle can be transferred at a time, nor how the interference of the mechanism with the bottles that are advancing in the cross conveyor during the return period is avoided. This type of pusher apparatus with combined mechanisms of cam and connecting rod-crank more commonly used, has the virtue of being simple and of easy adjustment but on the other hand, it has certain disadvantages. There is no control to present the last bottle of a group to be transferred from being intercepted too near the end of the pusher rod causing the bottles to deviate from the desired path. The cam which produced the vertical movement requires good lubrication or else irregular movements could be induced that cause bottles to fall over. The velocity of the pusher rod is considerable at the moment of making contact with the bottles.
From the above analysis of the state of the prior art, pusher apparatus, it can be observed that practically all of the pushers to date try to improve the operation velocity and to impart a softer path by means of more or less elaborate mechanisms. Practically all the known pushers travel in a path controlled by means of special designed cams whose shape is dictated by the desired path, the shape or slimness of the bottles, the production velocity, etc. The problems caused by the use of such cams are well known. These are mainly, that due to continuous exposure to considerable stresses to move heavy mechanisms at relatively high velocities, the cam surfaces and shaft suffer fast and considerable wear making it necessary to stop the machine and the pusher apparatus to carry out adjustments or change the cams. Furthermore, the cams require continuous lubrication and cleaning, in order to function adequately. On the other hand, said pusher apparatus operated by cams, necessarily require a motor working in strict synchronism with the functions of the machine. When the motor is too fast or too slow there is no way to correct it unless the machine is stopped. Another important disadvantage of cam operated pusher apparatus is the lack of flexibility because no adjustments can be made during operation of the machine to change the transfer path to account for changes in the type or diameter of the articles. The machine must be stopped to change or adjust the cams and its other mechanisms in order to operate with different kinds of articles. Needed adjustments in the path due to deviations or misadjustments of the cams or mechanisms are not possible when the pusher is operating. Still another disadvantage of prior art apparatus is the lack of flexibility as to the possibility of modifying the velocity and acceleration of the mechanisms because these are driven by a motor whose synchronism is strictly regulated by the machine and velocity and acceleration are defined by the design of the cams. Taking into account the limitations of the paths and article transfer apparatus of the known prior art and considering as the main technological dimensions the number of thrown or tipped over articles, which depends on factors such as the form of the articles (the slimner the article the greater the loss is), the production velocity (the greater the number of cycles of the pusher per minute, the greater the loss is) and the synchronism among the components of the apparatus, initial cost, velocities and feeding ranges, range of articles that can be handled (shape, diameter), selectivity, distance between the articles and range of adjustments that can be made, maximum impact allowed, maximum acceleration permitted and width of the lehr, research was carried out to find an optimal path of an article transfer apparatus which could overcome all the limitations of the previous pusher apparatus.
Taking the number of bottles knocked over as one of the technological considerations of greater importance, mathematical models were formulated to obtain the maximum velocity of the pusher rod at the moment of its impact against the containers and the maximum acceleration during the pushing path, such that for values lower than maximum, it could be insured that the pusher does not topple the containers by impact or by accleration. The models first considered the containers as ideal cylindrical test tubes, friction was neglected and a perfectly elastic impact was assumed. These assumptions represented more unfavorable conditions than the real ones and therefore the specifications obtained with said models were considered conservative. As the next step, experimental information was obtained which allowed an improvement of the above-mentioned specifications. Thus, the center of mass and rotation radius of those containers which had been considered of importance, because of production or sales volume was obtained and the static and dynamic friction coefficient between the containers and a conveyor such as those used in production was determined at different temperatures both in the transverse and longitudinal directions of the conveyor. These coefficients were also obtained for a steel plate carrying out tests at different temperatures. Also determined were restitution coefficients for a hard strip of asbestos and for a soft cover of the same material used to cover the transfer rod to avoid thermal impact on the containers. New mathematical models were then formulated taking into account friction and the restitution coefficients thus establishing new permissible maximum values for velocity and acceleration of the pusher arm for each of the selected containers. From these values it was possible to determine curves of time against velocity and position of the transfer arm which defined the kinematics of the path and device of the present invention. All these investigations have as a result an article transfer system in which the transfer rod describes an optimal path with specific velocities and accelerations, which practically reduce to zero the number of knocked-over articles during their transfer to the lehr independently of the type of pusher apparatus that could be used for such purpose.